319 - A Rare Presentation of Necrotizing Immune-Mediated Myositis Triggered by Statin Medication: A Case Report

Case Diagnosis: Necrotizing immune-mediated myositis (NIM) is a rare autoimmune disorder characterized by aberrant immune responses targeting skeletal muscles. Antibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) have been associated with NIM, distinguishing it from statin-induced myopathy. This case presents a patient initiated on statin therapy who developed muscle weakness and pain, leading to the diagnosis of NIM.

Case Description: A 41-year-old woman with intellectual disability, congenital hypothyroidism, and hyperlipidemia presented to the University of North Carolina emergency room with diffuse skin rash, joint pain, and muscle weakness progressive over one month. Notably, she had recently started statin therapy. Clinical examination revealed proximal muscle weakness, elevated liver enzymes, and creatinine kinase (CK) levels of 47,287. Electromyography showed myopathic motor units, and later muscle biopsy showed necrotic and regenerating muscle fibers. Serum anti-HMGCR antibodies were detected confirming statin induced NIM. Statin therapy was discontinued, and the patient received high-dose steroids, IVIG, and inpatient rehabilitation. She showed only marginal functional improvement despite decreasing and plateauing of CK values but was able to discharge home with family support.

Discussions: NIM, linked to anti-HMGCR antibodies, typically presents with progressive proximal muscle weakness and tenderness. The pathogenesis involves immunogenetic predisposition, with statin exposure leading to neoantigen formation. NIM is often misdiagnosed and can manifest with extramuscular symptoms.

Conclusions: This case underscores the importance of considering NIM in patients with unexplained muscle weakness, particularly in the context of statin use. Timely diagnosis and multidisciplinary treatment, including steroids, IVIG, discontinuation of statin therapy and rehabilitation, can improve outcomes. Healthcare providers should remain vigilant for this rare but debilitating condition when assessing patients with similar clinical presentations and medication histories.